Spectrometer flip top sample head

ABSTRACT

A spectrometer sample head including a housing, at least one source of radiation in the housing, and a flip top sample cell including first and second hinged plates and a window through the first plate with a pane in the window, the pane for receiving a sample thereon. The housing includes a channel for receiving the plates when coupled together for placing the sample in the optical path of the radiation.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/321,399 filed Jan. 20, 2009 and hereby claims the benefit of andpriority thereto under 35 U.S.C. §§119, 120, 363, 365, and 37 C.F.R.§1.55 and §1.78, and is incorporated herein by reference.

FIELD OF THE INVENTION

The subject invention relates to spectroscopy and the means to introducesamples for analysis using minimal preparation.

BACKGROUND OF THE INVENTION

Spectroscopic analyzers are used in a variety of applications. Forexample, infrared analyzers are used to monitor various fluids such asdairy products, fuels, oils, lubricants, in addition to solids,aerosols, gases, and the like.

The primary components of the applicant's infrared analyzer include asource of infrared radiation, typically a filament, which directsinfrared radiation through a sample held in a cell. After passingthrough the sample, the infrared radiation enters an analyzer includinga wedge conditioner, a reflective grating, and a detector assembly. Theoutput of the detector assembly is input to a processor programmed withalgorithms used to determine the different components of the sample. Theresults can be depicted on a display linked to the processor.

Absorption of certain infrared frequencies by the sample is indicativeof different components in the sample. See U.S. Pat. Nos. 6,289,149;5,856,870; and U.S. patent application Ser. No. 11/347,482 allincorporated herein by this reference. Additional prior art includesU.S. Pat. Nos. 5,470,757 and 5,764,355 also incorporated herein by thisreference.

Various sample heads or cells are known. In one example, a syringe isused to inject a small quantity of oil into a sample cell. Typically,such a cell has ˜100 microns thickness. In this case, since the samplecell is filled and not accessible for cleaning, solvent must beintroduced in to the cell to remove any remaining sample. The solventmust then be removed from the sample cell which requires forced air.This entire process requires solvent processes to ensure the cell isproperly cleaned, and significant time to perform the procedureproperly. Moreover, in the field, technicians may not have the skill ortime required in order to ensure a proper cleaning process.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a novel samplehead for a spectrometer which is easier to clean and yet still allowsfor quantitative analysis by ensuring a predetermined cell thickness.

It is a further object of this invention to provide such a sample headwhich is easy to use.

It is a further object of this invention to provide such a sample beadwhich is reliable.

It is a further object of this invention to provide such a sample headwhich is rugged.

The subject invention results from the realization, in part, that anovel, easy to use sample head for a spectrometer includes a flip topsample cell with two hinged plates separable to place a sample on oneplate window and, when coupled together, define a sample chamber of apredetermined thickness.

This invention features a spectrometer sample head including a housing,at least one source of infrared radiation in the housing, and a flip topsample cell including first and second hinged plates each including awindow aligned with each other when the plates are coupled together. Thehousing includes a channel for receiving the plates when coupledtogether for placing a sample in the optical path of the radiation.Typically, the windows are mounted flush in their respective plates.

In one embodiment, there is a seal about one said window. Also, oneplate includes a plurality of kinematic mounts (e.g., 3) providing apredefined spacing between the windows, e.g., 100 microns.Alternatively, the kinematic mounts are adjustable. At least one platemay include a magnet set therein for releasably coupling the plates andpreferably there are four spaced magnets in the first plate and fourspaced magnets in the second plate. The housing channel may include atleast one edge groove and at least one plate includes a depending shoewhich slides in the edge groove. In the preferred example, the channelincludes opposing edge grooves and one said plate includes spaced hingedmembers each including a shoe. There may be two sources in the housing.The typical sample head further includes a coupler for joining thesample head to a spectrometer.

The subject invention also features a sample cell comprising a housingincluding a channel therein, a source of radiation in the housing, and aflip top cell received in the channel of the housing. The flip top cellincludes first and second hinged plates each with a window aligned witheach other when the plates are coupled together. The plates areseparable when the flip top sample cell is drawn up out of the channelin the housing to place a sample on one said window.

The subject invention also features a flip top sample cell includingfirst and second hinged plates each including a window, the windowsaligned with each other when the plates are coupled together. The platesare separable for placing a sample on one said window.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a schematic three-dimensional side view of an example of aninfrared spectrometer sample head in accordance with the subjectinvention;

FIG. 2 is a schematic three-dimensional rearward view of the sample headshown in FIG. 1;

FIG. 3 is a schematic three-dimensional front view of the sample headshown in FIGS. 1 and 2;

FIG. 4 is a schematic three-dimensional side view showing the samplehead of FIGS. 1-3 with the flip top sample cell thereof in its outwardposition;

FIG. 5 is a schematic three-dimensional front view of the sample cellshown in FIG. 4;

FIG. 6 is a schematic three-dimensional rearward view of the sample cellshown in FIGS. 4-5;

FIG. 7 is a schematic three-dimensional top view showing the flip topsample cell in its decoupled or open configuration;

FIG. 8 is a highly schematic block diagram showing the primarycomponents associated with an example of a spectrometer sample head inaccordance with the subject invention;

FIG. 9 is another highly schematic block diagram showing the primarycomponents associated with another example of a spectrometer sample headin accordance with the subject invention;

FIG. 10 is a schematic exploded front view showing an example of asample head channel which receives the flip top sample cell;

FIG. 11 is an exploded assembly drawing of an example of a sample cellhead in accordance with the subject invention;

FIGS. 12A and 12B are schematic views of a top plate for the sample cellhead of FIG. 11;

FIG. 13 is a schematic view of the bottom plate for the sample cell headof FIG. 11; and

FIG. 14 is a schematic view of an embodiment where the kinematic mountsare adjustable; and

FIG. 15 is a schematic view of a calibrator holder for calibrating thesample cell using interference fringe techniques.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

FIGS. 1-3 show an example of spectrometer sample head 10 in accordancewith the subject invention. Housing 12 includes a source of infraredradiation therein, typically a filament producing radiation in the rangeof 900 to 4,000 cm⁻¹.

Flip top sample cell 14 includes hinged plates 16 a and 16 b, FIG. 3shown in position in FIGS. 1-3 within housing 12 and coupled togetherfor spectral analysis. Sample head 10 also includes coupler 18 forjoining sample head 10 to a spectral analyzer and electrical connection20 for energizing and controlling the infrared source within housing 12.

FIGS. 4-6 show flip top sample cell 14 urged upwards out of housing 12and a window 30 a in plate 16 a aligned with window 30 b in plate 16 b.Typical material for windows 30 a and 30 b is ZnSe and the windows aretypically 13 mm in diameter and 2 mm thick.

FIG. 7 shows plates 16 a and 16 b decoupled and spread apart so that asample can be placed on window 30 a of plate 16 a. FIG. 7 also showsmore clearly hinges 40 a and 40 b at the bottom corners of plates 16 aand 16 b, channel 42 in housing 12 configured to receive plates 16 a and16 b when coupled together, and handles 44 a and 44 b for coupling anddecoupling plates 16 a and 16 b, spreading them apart, urging thecoupled plates down in channel 42, and withdrawing them out of channel42.

In one embodiment, seal 46 (e.g., an O-ring) is disposed about window 30a to ensure that the sample is captured when placed into position foranalysis. Kinematic mounts 48 a-48 c in plate 16 b provide a predefinedspacing (e.g., 100 microns) between windows 30 a and 30 b when plates 16a and 16 b are coupled together. To keep plates 16 a and 16 b coupledtogether once a liquid sample has been placed on window 30 a and tomaintain the sample thickness desired, plate 16 b includes magnets 50a-50 d of one polarity and plates 16 a includes magnets 52 a-52 d of theopposite polarity. Plates 16 a and 16 b are typically made of aluminumand have a surface flatness of L 0.005 inches in the area where theycouple together. Windows 30 a and 30 b are preferably mounted flush withthe surface of the plates to (a) prevent any sample from becoming lodgedin the sample head and (b) to allow easy removal of sample materialusing only a wiping action across each plate.

In use, the sample head is fitted to a spectrometer, the flip top cellis urged up and out of housing 12, plates 16 a and 16 b are decoupled asshown in FIG. 7, and a liquid or solid sample is placed on window 30 a.Then, plate 16 b is swung over on top of plate 16 a whereupon magnets 50a-50 d countersunk in plate 16 b are attracted to magnets 52 a-52 dcountersunk in plate 16 a releasably coupling the two plates together.Kinematic mounts 48 a-48 c in plate 16 b provide a slight separationbetween plates 16 a and 16 b and together with the geometry of theplates and windows 30 a and 30 b define a spacing of 100 microns (or anyother desired spacing) between the windows. The coupled together platesare then urged down into channel 42 in housing 12 as shown in FIGS. 1-3for analysis of the sample.

FIG. 8 schematically depicts plates 16 a and 16 b coupled together and a100 micron thick sample 60 between windows 30 a and 30 b. IR source 62emits radiation 63 which passes through window 30 a, sample 60, andwindow 30 b. Thereafter, the radiation proceeds to analyzer 64 which maybe engineered in accordance with U.S. Pat. Nos. 6,289,149; 5,856,870;and/or U.S. patent application Ser. No. 11/347,482. The sample head ofthe subject invention, however, may be used in connection with otherinfrared analyzers and even analyzers based on other spectrums ofelectromagnetic energy, (e.g., visible light, ultraviolet light, and thelike).

FIG. 9 shows a sample head configuration with two infrared sources 62 aand 62 b. Each includes a filter 68 a, 68 b and beam splitter 70 directsinfrared radiation from both sources to window 30 a in plate 16 a. Thesources, beamsplitter, and filters are preferably configured such thatfrom each source, a defined and separate infrared frequency band entersthe spectrometer. In this way, the bandwidth of the spectrometer can besignificantly increased relative to using only one frequency band. Thesources are then excited in a fashion such that only one frequency bandenters the spectrometer at a given time.

Although there are a variety of available designs for the placement ofthe flip top sample cell within the sample head housing, FIG. 10 showsone configuration where hinges 40 b and 40 a for plates 16 a and 16 beach include a depending shoe 80 a, 80 b sliding in edge grooves ortracks 82 a, 82 b, respectively, of sample head housing channel 42. Theedge grooves 82 a, 82 b stop short of the top of the channel in thisexample to prevent the flip top cell from being completely withdrawn outof the sample head housing channel.

FIGS. 11-13 show an example of a sample cell head in accordance with thesubject invention where housing 12 includes the two sources 62 a and 62b of radiation held by holder 100 via clamps 102 a and 102 b alsosupporting BBP filters 105 a and 105 b. Channel 42 for flip top samplecell 14 is defined by holder 108.

FIG. 12A shows three steel inserts in top flip top cell plate 16 bforming the kinematic mounts and the magnets 50 a-50 c. FIG. 13 showstwo O-ring seals 46 a and 46 b surrounding window 30 a flush withinbottom plate 16 a. Otherwise, the references correspond to FIGS. 1-7discussed above.

In another example, kinematic mounts 48 a-48 c, FIGS. 7 and 12 areadjustable and O-ring 46, FIGS. 7 and 13, is optional. FIG. 14 showsscrews 110 a, 110 b, and 110 c in plate 16 a, the distal ends of whichcan be adjusted relative to plate 16 b. By varying the position ofscrews 110 a-110 b, the distance between windows 30 a and 30 b varies.Indeed the distance between plates 16 a and 16 b can be varied, and sotoo can the orientation between the plates, e.g., parallel to each otheror non-parallel to each other, for calibration.

FIG. 15 shows a wrench 112 being used to adjust one kinematic mountscrew through an opening 114 in calibration holder 118. One preferredcalibration procedure is as follows. First, the windows are cleaned tobe free of oil. Next, the three set screws 110 a-c are backed out sothat when the cell is held up to a light whilst closed, no light isvisible through the plates. A Harrick 100 micrometer spacer is placed onthe window plate with the three screws and close the cell is closedgently onto the spacer. The screws are tightened clockwise so they arejust touching the plate then backed off a ¼ of a turn. An easy way to dothis is to place the wrench small side into a screw and then rotate thecell body anticlockwise toward you. As soon as the screw bite onto theapposing surface, the wrench will stop turning and it will need to bebacked out a quarter turn. Repeat for the remaining two screws. The cellis then placed into calibration holder 118, FIG. 15 with the screwsfacing out for interferrometic analysis. Tall fringes should be clearlyvisible in the interferogram. If they are not visible or are very smallcheck that the set screws are sufficiently backed out, the window isclean and the spacer is seated correctly on the ZnSe window. If thefringes are still small and not clearly defined the spacer should berepositioned in a different position on the window. Place the alienwrench in one set screw so that the long end of the wrench is pointingas close to vertically up as possible (this will depend on the locationof the screw and where it was adjusted in the previous step). If theprevious step was followed correctly, one should be able to turn thewrench freely a bit in both directions so the wrench falls under its ownweight under gravity and it can be supported with a finger. When thescrew bites onto the opposing surface, the fringe in the check signalwill drop in height and the wrench will remain supported under its ownweight. The fringe height should be reduced by 50% so an additionalamount of force other than the weight of the wrench may be required.Next move onto the second screw and place the wrench as close tovertical as before and adjust the screw in the same way. When this screwbegins to bite, one should see the fringe begin to decrease inintensity. Stop turning the screw until it just begins to disappear intothe interferogram. Note if the fringe starts to get taller again whenthis screw is tightened, back off the screw to its original position andrepeat this step with the third screw and the fringe should decrease inheight in this scenario. Move onto the third screw place the wrench invertical position as before so gravity can be used to engage screw intoplate. As soon as screw begins to engage, the fringe should begin toreappear and grow again. Turn the screw until about the same size fringeis recorded at the end of the step above. Remove the wrench and take thecell out of the holder, open the cell and remove the spacer. Carefullyclose the cell and place it back in the holder. Ensure that the fringeis still visible and approximately the same height as before. Thefixture now needs to be removed from the sample compartment. Flip thefixture over and place a finger over the cell and apply pressure to thetop of the cell to stop it from falling out and also to keep itreferenced against the bottom of the cell compartment. Place the wrenchso it falls into one of the labeled sectors; 00, 0, 1 or 2 labeled nearscrew as shown in FIG. 15. The exact location of the wrench will dependon the position that was set previously. When the wrench is located intothe screw head, it sits in the middle of sector 2. Turn the wrenchclockwise very slowly so it lines up with the line bordering the nextsector (in this case sector 3). This is done by holding the fixture upto eye level and we stop turning the wrench as soon as the line at thebeginning of the next sector cannot be seen. This sets the startingposition for this screw. Note down the sector position of the wrench forreference later. Note if the wrench comes to lie on the border of asector to begin with it will need to be rotated to the next sector. Ifthe screw lies on the border of sector 2 and 3 then it will need to beremoved and placed so it is located before sector 00. Also, it may beeasier to rotate the fixture clockwise if the wrench falls into one ofthe other not so horizontal positions. This makes it easier to line upthe wrench with the lines. Remove the wrench from the screw carefullywith the cell and holder in the same position. If the cell is flippedover, there is a chance that the wrench will turn which is why we removeit in this position in this step. Place the cell holder back in thesample compartment. The fringe should still be visible in the checksignal screen. If the screw was turned a whole sector in the previousstep, it may need to be clockwise to bring the fringe back. We now wantto adjust the next screw so that we get a minimal fringe height that canstill be detected by the calibration program. Turn the screw that madethe fringe reappear clockwise to make fringe bigger and anticlockwise tomake fringe smaller. Remember you need to have the fringe as small aspossible. Once an adjustment is made by either turning the screwclockwise or anticlockwise, the fringe must move from its previousposition in the check signal screen, either by whole fringe moving leftor right or the fringe height changing. This is important because if itdoesn't respond to a screw turn then the screw is no longer in contactwith the opposing surface. It is important to make the fringe as smallas possible as this will have benefits later in the procedure. Take aclean cell background and measure the path length. If an error appearsand the cell path length is not computed then the fringe is not tallenough and you will need to go back and apply further clockwise rotationon the screw to make the fringe taller. If the cell path length iscomputed without any problems, note the number calculated inmicrometers. Note it is often best to start with a very small fringethat fails then with minor adjustments make the fringe taller so itpasses. As has previously been mentioned this will reap benefits laterin the procedure when we evaluate the degree of fringing based on thewedge. Remove the holder and turn it upside down whilst holding the cellin place. Place the wrench carefully into the position noted before. Oneshould still not be able to see any of the sector line. Carefully turnthe wrench a further six sectors (90° from start position) and line upthe edge of the wrench with the final sector line as before and stopturning the wrench when the line can no longer be seen. By turning thewrench 90°, an additional 16 micrometers of path length is induced intothe cell and an optical wedge is produced which will totally eliminatethe effects of fringing. Very carefully remove the wrench from the setscrew as before with the holder upside down as before. Place the cellholder back into the sample compartment and view the interferogram. Oneshould not see any evidence of a fringe. As a further more importantcheck, view the power spectrum and zoom in the area to the left of theCo₂ absorbance band. One should notice minimal fringing noise in theregion of the power spectrum. If too much noise does still exist, goback a few steps and reset fringe correction and try to minimize thefringe height. Next, place two drops of 5606 hydraulic fluid onto thewindow with the screws using a plastic pipette. Very gently andcarefully close the cell making sure not to induce any air bubbles.Place the cell in the holder with the screws facing to the right. Afterthe analysis is completed, record the results.

Interference fringes have traditionally been used to very accuratelyderive parallel cell path length. In a parallel cell, the distance fromthe interfering secondary centerburst (fringe) to the centerburst isequal to the path length of the cell. The distance between interferogrampoints can be accurately derived knowing the wavelength of themonochromatic reference laser. This theory is used to derive theparallel path length and also the wedged path length in this procedure.The wedged distance is derived by calibrating the angular rotation ofthe fine pitch screws into micrometers. When a single screw is rotatedinto the apposing plate the two surfaces move apart and a wedge isformed between the plates pivoting on the other two screws. Thedifference in the fringe location is equal to the change in path lengthcaused by the rotation of a screw-calibration of a 15 degree turn forthree different screw locations resulted in an average 2.7 micrometerchange in actual path length. It's not possible to measure the travel ofa fringe for 90° of rotation which is required to sufficiently removefringing because the fringe disappears. So, instead we can just sum six,¼ turns equating to 16.2 micrometers in path length change.

We can also prove that this additional wedged dimension is correct byusing an optical microscope to derive the distance that a ¼ turn of ascrew equate to. Using this distance and the geometry of the cellenables the wedged distance to be easily calculated using basictrigonometry. The surface features of the flat head of the screw arefocused in on using a ×1000 magnification lens using a calibrated 1micrometer focus wheel. The difference in the position of the focuswheel (in micrometers) when the screw is turned out a further ¼ turn andre-focused is equal to the distance traveled by the screw. Calibrationof the travel of the screw with a ¼ turn using this method resulted in aconsistent distance of 49 micrometers using different ¼ turns on thecell holder. A ¼ turn of one fine pitch screw also produces anadditional 16.3 micrometers of wedged path length on top of the originalparallel path length.

The result, in any embodiment, is a sample head for a spectrometer whichautomatically ensures a predefined sample thickness. The sample head ofthe subject invention is also easy to use, reliable, and rugged.

Thus, although specific features of the invention are shown in somedrawings and not in others, this is for convenience only as each featuremay be combined with any or all of the other features in accordance withthe invention. The words “including”, “comprising”, “having”, and “with”as used herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

Finally, other embodiments will occur to those skilled in the art andare within the following claims.

What is claimed is:
 1. A flip top sample cell comprising: a first platewith a flat interior surface; a second plate with a flat interiorsurface; a hinge coupling an edge of the first plate to an edge of thesecond plate so the plates can be coupled together and separated fromeach other; a window in the first plate flat interior surface; a windowin the second plate flat interior surface aligned with the window in thefirst plate when the plates are coupled together; a pane over the windowin the first plate; and a pane over the window in the second plate. 2.The flip top sample cell of claim 1 in which at least one said plateincludes at least one spacer configured to space said panes apart whensaid first plate is coupled to said second plate.
 3. The flip top samplecell of claim 2 in which said spacer is a kinematic mount.
 4. The fliptop sample cell of claim 3 in which said kinematic mount is adjustable.5. The flip top sample cell of claim 1 in which at least one said plateincludes a magnet releasably coupling said plates together.
 6. The fliptop sample cell of claim 1 in which at least on said plate includes atleast one adjustable kinematic mount configured to space said panesapart when said first plate is coupled to said second plate and in whichat least one said plate includes a magnet releasably coupling saidplates together.
 7. A flip top sample cell comprising: a first platewith a flat interior surface; a second plate with a flat interiorsurface; a hinge coupling an edge of the first plate to an edge of thesecond plate so the plates can be coupled together and separated fromeach other; a window in the first plate flat interior surface; a windowin the second plate flat interior surface aligned with the window in thefirst plate when the plates are coupled together; a pane over the windowin the first plate; a pane over the window in the second plate; and atleast one said plate includes at least one spacer configured to spacesaid panes apart when said first plate is coupled to said second plate.8. The flip top sample cell of claim 7 in which said spacer is akinematic mount.
 9. The flip top sample cell of claim 8 in which saidkinematic mount is adjustable.
 10. The flip top sample cell of claim 7in which at least one said plate includes a magnet releasably couplingsaid plates together.
 11. A flip top sample cell comprising: a firstplate with a flat interior surface; a second plate with a flat interiorsurface; a hinge coupling an edge of the first plate to an edge of thesecond plate so the plates can be coupled together and separated fromeach other; a window in the first plate flat interior surface; a windowin the second plate flat interior surface aligned with the window in thefirst plate when the plates are coupled together; a pane over the windowin the first plate; a pane over the window in the second plate; and atleast one magnet releasably coupling said plates together.
 12. The fliptop sample cell of claim 11 in which at least one said plate includes atleast one spacer configured to space said planes apart when said firstplate is coupled to said second plate.
 13. The flip top sample cell ofclaim 12 in which said spacer is a kinematic mount.
 14. The flip topsample cell of claim 13 in which said kinematic mount is adjustable. 15.A spectrometer sample head comprising: a housing; at least one source ofradiation in the housing; and a flip top sample cell including first andsecond hinged plates; a window through the first plate with a pane insaid window, said pane for receiving a sample thereon; the housingincluding a channel for receiving the plates when coupled together forplacing a sample in the optical path of the radiation, the channelincluding at least one edge groove and at least one plate including adepending shoe which slides in the edge groove.
 16. The spectrometersample head of claim 15 in which the channel includes opposing edgegrooves and one said plate includes spaced hinged members each includinga shoe.